We will continue our studies of crystalline complexes of aspartate aminotransferase with L-glutamate, L-aspartate, Alpha-methylglutamate, Beta-hydroxyaspartate, phosphoserine, cysteic acid, and other amino acids. We will measure polarized light-absorption spectra and determine equilibrium constants for the enzyme in the crystalline state. We will also diffuse substrates and inhibitors into preformed crystals and will ascertain the best conditions for determination of electron density difference maps by x-ray diffraction. Various analogs of pyridoxal-P will be used to replace the natural coenzyme in another series of experiments. We will complete current studies of the reaction of pyridoxal 5'-sulfate and aspartate aminotransferase. A cross-linked peptide formed by peptic digestion of the modified enzyme will be characterized. Characterization of the labile, low-molecular weight product formed by reaction of serine sulfate and glutamate decarboxylase will be completed. The reaction of a 5'-vinylphosphonic acid analog of pyridoxal-P with substrate in the active site of glutamate decarboxylase will be studied. The band shapes of absorption spectra of Schiff bases, enzymes containing pyridoxal phosphate, and visual pigments will be examined. Spectra will be fitted with lognormal distribution curves and microscopic dissociation constants will be estimated. Special attention will be paid to analysis of spectra of enzyme-substrate complexes.